While not necessarily limited thereto, the present invention is particularly adapted for use as a mechanical seal for a fluid coupling which enables liquid to be transferred between two relatively rotatable parts. The inner part of the coupling, which has a central bore extending therethrough for conveying fluid under high pressure, is disposed within a cylindrical outer part closed at one end by a cover. The central bore in the inner part which conveys fluid under high pressure merges into at least one radial bore which opens into a recess disposed on the periphery of the inner part. This recess, in turn, is adapted to be connected to a port in the outer cylindrical part.
In copending application Ser. No. 217,618, filed Dec. 18, 1980 and assigned to the Assignee of the present application, a mechanical seal for a fluid coupling is shown comprising an inner part rotatable within an outer part. The inner part has one or more radial bores which extend from a central passageway conveying fluid under high pressure to its periphery where the radial bores are adapted to communicate with ports in the outer part. A large diameter portion of the inner part is exposed at both ends to a sealing fluid which is compressed by a cylindrical piston acted on by high-pressure fluid within the central bore of the inner part. Consequently, the pressure of the sealing fluid is always equal to that of the high pressure fluid.
Since the sealing fluid in the apparatus of copending application Ser. No. 217,618 is at the same pressure as the high-pressure fluid, the high-pressure fluid cannot be prevented from flowing into the chamber filled with the sealing fluid. As a consequence, it is possible, particularly after prolonged operation, for the high-pressure fluid to reach the aforementioned chamber containing the sealing fluid where it will form an emulsion which no longer has the properties of a sealing fluid and cannot reliably seal the device.